The present invention relates to an emulsion of a polymer having a (meth)acrylate unit and adhesive compositions containing the emulsion. More specifically, it relates to a polymer emulsion which reacts to be fixed on the surface of a solid containing a polyvalent cation reactive with a sulfonic acid group, such as a hydroxyapatite structure, cement, a metal compound or a mineral, an adhesive film from the polymer emulsion formed on the surface of said solid and an adhesive composition which exhibits excellent adhesion to a substrate.
The above adhesive film exhibits excellent adhesion to a tooth and excellent sealability to dental tubules, so that it can be suitably used as a dental primer and a dental anti-hypersensitivity film.
For treating a hydroxyapatite structure such as a dentin for remedy, an adhesive material such as 4-META/MMA-TBB (Superbond, supplied by Sun Medical Co., Ltd) has been hitherto used. The adhesive material is bonded by a method in which a drilling dust is removed by preliminary etching of an adherend surface with an acid, the adhesive material is applied and cured and then a radical-polymerizable acrylic resin is filled and cured. Since, however, the acid used for the above acid treatment is a low molecular weight compound, it may infiltrate deep into the hydroxyapatite structure. Therefore, when a dentin is treated for remedy, the acid comes to remove a healthy part of the dentin as well and sometimes reaches a dental pulp to attack the nerve and give an acute pain.
Therefore, when a portion near to a dental pulp is treated for remedy, there has been conventionally employed a method in which the attack in bonding is prevented by applying onto the above portion a carboxylate cement which is a combination of a polymer type polyacrylic acid with zinc oxide or a glass ionomer cement which is a combination of a homopolymer of polyacrylic acid or a copolymer from acrylic acid and either itaconic acid or maleic acid with aluminosilicate glass.
Since, however, these cements are very poor in adhesion, there have been problems such as secondary caries and coming off of the attachment for remedy.
For the therapeutical treatment of the hypersensitivity of a dentin based on exposure of dental tubules in the mouth, there are used a liniment of silver nitrate, potassium oxalate or disodium hydrogenphosphate/calcium chloride (Ikemura, Imai, Journal of Japanese Dentistry Preservation Society, vol. 35, 26 (1992)), a toothpaste containing citric acid or sodium citrate, a glass ionomer cement and a 4-META-containing adhesive resin (D liner, supplied by Sun Medical Co., Ltd).
The above preparations against the hypersensitivity of a dentin have the following advantages. The liniment is free of stimulation to a dental pulp and coloring, and the toothpaste obviates the therapeutical treatment in a dentist's chair. However, it is usual that it takes a long period of time before they exhibit their effects. The polymer type carboxylic acid such as glass ionomer hardly affects a dentin. However, it is poor in adhesion to a dentin and resistance to water, and its effect does not continue satisfactorily. On the other hand, the adhesive resin shows its effect, but is used for the therapy by a method in which a portion to be treated is preliminarily etched with a low molecular weight acid such as a 10 citric acid--3% ferric chloride aqueous solution or the like, and a solution prepared by mixing a curing agent and a monomer immediately before use is applied and polymerized. Therefore, it still involves a problem in the influence of the low molecular weight compound on a dentin and handling.
Further, VARNAL.RTM. (CETYLITE INDUSTRIES INC. (U.S.A.)) is commercially available, which is used for alleviating the cervical hyperesthesia by applying it in the form of a solution to the dental surface of cervical hyperesthesia and drying it to form a film. This method of treating a tooth surface is similar to that employed in the present invention. However, VARNAL is a solution prepared by dissolving a copal resin which is a natural resin in an alcohol solvent, and is basically different from the present invention in the following points: VARNAL does not contain any sulfonic acid group which is an essential component for the emulsion of an emulsion-polymerizable polymer of the invention, it may not be facile to acquire the copal resin since it is a natural resin and difficult to synthesize, and VARNAL is poor in adhesion to a tooth.
For decreasing the infiltration of an acid into a hydroxyapatite structure and imparting it with affinity to an acrylic resin, the present Applicant has proposed an acrylate copolymer containing a sulfonic acid group which allows to ion-bond or chelate-bond to a calcium component of the hydroxyapatite structure (Japanese Laid-open Patent Publications Nos. 171,024/1985 and 261,442/1990).
The polymer disclosed in the above Japanese Laid-open Patent Publications is specifically an acrylic copolymer produced from methacrylate such as methyl methacrylate and a sulfonic acid group-containing monomer such as p-styrenesulfonic acid and/or methacrylate macromer having a vinyl group at its terminal such as methyl polymethacrylate. These Publications disclose a method in which the above acrylic copolymer is dissolved in a solvent such as water or ethanol, the resultant solution is applied directly to a hydroxyapatite structure surface without acid etching and the resultant coating is washed with water. In this method, the degree of infiltration into the hydroxyapatite structure is small, the copolymer firmly bonds to the hydroxyapatite structure since the sulfonic acid group bonds to a calcium component of the hydroxyapatite structure, and the hydroxyapatite structure can be bonded to an acrylic resin to form a layer thereon since the polymethyl methacrylate portion of the acrylic copolymer and the acrylic resin have good affinity.
However, further studies of the above acrylic copolymer have revealed the following. When a solution of the acrylic copolymer is applied and dried without washing it with water, the acrylic copolymer sometimes shows no adhesion force due to a presence of a remaining unreacted acrylic copolymer which does not react with the hydroxyapatite structure. It is therefore essential to carry out a step of washing with water for obtaining a stable adhesion force.
It is an object of the present invention to provide a novel adhesive emulsion to overcome the above problems and an adhesive composition containing the same.
It is another object of the present invention to provide a novel adhesive emulsion which decreases the infiltration into an adherend, like a conventional sulfonic acid group-containing copolymer, which exhibits an adhesion force to a hydroxyapatite structure, a cement, a metal or a mineral when it is applied thereto and, without washing it with water, only dried around room temperature to form a film, which exhibits excellent affinity to a radical-polymerizable acrylic resin composition, and which further permits sealing the surface of a hypersensitive dentin since a film formed therefrom has the property of bonding to a dentin which is a hydroxyapatite structure.
Other objects and advantages of the present invention will be apparent from the following description.